Some of the determinants of the rate of synthesis of prostaglandins, i.e., release, will be examined in terms of their effects on vascular reactivity, organ blood flow and its partition and salt and water balance. Preparations of varying complexity will be used: sections and sleeves of blood vessels, in situ and isolated kidneys and unanesthetized animals. Prostaglandin interrelationships with the kallikrein-kinin and renin-angiotensin systems will be explored. The effect of selected antihypertensive drugs on the level of activity of prostaglandins and their interrelationships with other vasoactive hormones will be determined.